Small information devices may receive information through a keypad and be controlled through the keypad. Input methods using a keypad are sufficient for limited and simple functions of typical information devices, such as input of a phone number or transmission of a text.
Recently developed optical scanning devices recognize a fingerprint or a bar code for improving user convenience and security. For example, a small pointing device using a finger skin is disclosed in Korean Patent Publication No. 10-2005-0002463. Light, emitted from a light emitting device, passes through a transparent plate through an incidence surface thereof and arrives at an object located on an opposite surface of the transparent plate to the incidence surface. Then, the light is reflected from the object. The light reflected from the object is transmitted to a light receiver part through a lens. As a result, the light receiver part recognizes an image of the object.
However, such typical optical scanning devices use an infrared LED and form an image using light absorbed and scattered by an object-side surface. Thus, a contrast ratio of an image formed at the light receiver part is low, which makes it difficult to obtain high resolution.